Semiconductor manufacturers continue to measure and control the level of contamination in the processing environment, especially during the critical steps of the photolithography processes. The typical means of determining the quality and quantity of contamination in gas samples in cleanroom manufacturing environments involves sampling air and purge gases, such as, for example, filtered and unfiltered air, clean dry air, and nitrogen. One of the most common base contaminants in the air worldwide is ammonia. Within a semiconductor fabrication facility ammonia commonly arises from wet benches, chemical vapor deposition (CVD), cleaners, Si3N4 and TiN deposition, and people. And, outside the semiconductor fabrication facility, farms, fertilizer and sewers are major sources of ammonia.
Contaminant measurement systems used in semiconductor environments are typically of the continuous, or semi-continuous, sampling variety or of the fixed sampling interval variety. A continuous or semi-continuous sampling system is installed in a cleanroom and operates in a substantially ON state whenever the facility is operating. Continuous and semi-continuous sampling systems are typically equipped with measurement and analysis systems for providing data on contaminant levels within the cleanroom. As such, continuous and semi-continuous sampling systems do not require removal from a cleanroom in order for an operator to obtain data regarding contaminant levels within the cleanroom environment. Since continuous and semi-continuous sampling systems produce results on site, they are often large, complex and expensive to acquire, operate and maintain. In addition, these systems require periodic calibrations to ensure that they operate properly in the environment. In contrast, samplers of the fixed interval variety are often portable and inexpensive since they only sample gases within a cleanroom. Fixed sampling interval devices are removed from the cleanroom for analysis of contaminants contained therein. Analysis can be performed by an end user of the devices or the sampling devices can be sent offsite for analysis. Fixed interval sampling devices are attractive to end users because they are relatively simple to operate; however, prior art fixed interval sampling devices have shortcomings.
For example, one traditional sampling approach for determining the concentration of cleanroom contaminants, especially ammonia, using fixed interval sampling devices has been through the use of wet impingers. These wet impinging approaches have certain drawbacks including accidental spillage of the scrubbing media (typically, deionized (DI) water or a DI water solution), accidental inversions of the impinger, and limits to sampling time (thereby imposing limits on the lower-detection-limit of the approach) due to natural evaporation of scrubbing media (DI water). In addition, wet impinger systems frequently require installation of the impinger by a highly trained technician. Another shortcoming associated with wet systems is that an end user typically has to wait more than a week to receive analysis results after sending the wet impinger system to an analysis facility. Furthermore, wet impinger systems can be prone to bacterial contamination of the liquid scrubbing media and wet impinger vials are often made of fragile glass or quartz making them prone to breakage during shipment. Consequently, there is an ongoing need for improvements in systems and methods for the measurement of contamination of gases used for industrial processes using fixed interval sampling devices that do not require wet impinger based sampling.